Drying Wood at Home

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by Eric Meier

Allowing lumber to passively sit at a given humidity level in order to obtain a desired EMC (air-drying) may be the simplest and least expensive method of seasoning wood, but it is also the very slowest. Drying times can vary significantly depending upon wood species, initial moisture level, lumber thickness, density, ambient conditions, and processing techniques.

Drying times and kilns

The traditional rule-of-thumb for air-drying lumber is to allow one year of drying time per inch of wood thickness; this adage obviously only takes a few of the aforementioned variables into account, but it’s at least a rough starting point in understanding the time investment required in order to properly air-dry lumber.

In situations where green wood is to be processed into usable boards, (especially in the case of thicker lumber), a kiln is frequently used to control the drying process. While there are various types of kilns used to dry lumber, the basic premise is usually the same: a large insulated chamber or room is used to balance and control humidity, temperature, and airflow to safely and efficiently bring wood down to an acceptable moisture content.

The main advantage of a kiln is that with the increased temperature and airflow—all while carefully maintaining and controlling the ambient humidity—the wood can be dried much more evenly, minimizing any sort of moisture gradient between the outer shell (which dries very quickly) and the inner core (which slowly equalizes moisture with the shell). Thus, a kiln is able to dry wood much more evenly, and it’s this uniformity in drying that allows it to also dry the wood quickly—simultaneously avoiding the drying defects usually associated with rapid, uneven drying.

Drying defects

But kiln drying may also introduce internal stresses into the wood—particularly if an improper kiln schedule is used, or if corrective measures are not employed—resulting in a condition known as case-hardening. This defect is caused when the outer shell begins to dry faster than the core: the shell tries to shrink, but is inhibited by the still-wet core. If the moisture difference between the core and the shell is too great, the shell can dry in a stretched condition. Later, as the core eventually begins to dry and shrink, the condition is reversed, and the stretched shell prohibits the core from completely shrinking. In extreme instances of case-hardening, the core can split and check in an irreversible condition called honeycombing.

This piece of Red Oak (Quercus rubra) exhibits honeycombing, which is among the worst of drying defects, both because it’s irreversible, and it usually can’t be detected by looking at the face of the lumber.

Kiln drying wood at elevated temperatures also has many other secondary effects as well, such as killing powderpost beetles (a destructive wood pest) in all stages of their development. However, it can also cause some woods—such as Black Walnut (Juglans nigra)—to lose the vibrancy of their heartwood colors, resulting in a more uniform and/or washed-out appearance.

For most woodworkers, running their own kiln to quickly dry lumber may be impractical or excessive. In most instances, simply storing project lumber at a targeted humidity level is the best option to ensure it will be at the correct EMC when building time comes. However, in some cases, such as when processing logs or other green wood into lumber, a more meticulous procedure will need to be followed.

Home air-drying tips

Process logs in a timely fashion. If a tree has just been cut down, or there has been recent storm damage, it’s best to process the logs into lumber as quickly as possible; doing so will help to open up the wood and aid in drying, which can prevent rot or stain from marring the wood. Bark on whole logs can act as a natural moisture-barrier, and if left unsawn, can contribute to fungal decay and deterioration in some species. A hallmark of poorly processed, do-it-yourself lumber is the presence of spalted or partially rotted wood.

Cut the wood slightly oversized. Remember that wood shrinks as it dries. This, along with the material that will inevitably be lost when the boards need to be jointed/planed smooth, mean that green wood should always be cut larger than the desired finished size. (And you usually don’t need to bother jointing/planing the wood prior to drying, since it will no doubt distort at least slightly during the drying process, and the edges should be dressed after the wood has dried to EMC—an exception to this is that two surfaces of a log should be jointed level to facilitate getting even and predictable cuts on the bandsaw.)

Seal the ends. In addition to processing logs in a timely manner to prevent stain and decay due to excessive moisture, the opposite is also to be avoided: allowing the wood to dry out too quickly will result in splits and endgrain checking. It is important to remember that moisture escapes from wood about 10 to 12 times faster on the ends than through other surfaces. Sealing the endgrain forces the moisture to exit in a slower, more uniform manner. If this is neglected, the ends will tend to shrink faster than the rest of the wood, creating tremendous stresses on the piece that’s ultimately only relieved with endgrain checks—a very common drying defect. (Although there are specially formulated endgrain sealers on the market, just about anything will do in a pinch: paraffin wax, polyurethane, shellac, or even latex paint can be used to seal the endgrain surface. The key is to build up a thick, obstructing film that will inhibit moisture from escaping at the ends of the board. In order to minimize the risk of checking, it is best practice to coat lumber ends within minutes—not hours or days—after coming off the saw.

Stack and sticker. Having lumber of uniform lengths and thicknesses greatly aids and simplifies the stacking process; once a log is sawn up into planks of satisfactory dimensions, it’s crucial to stack them in such a way that they will be exposed to air on all sides—stickers are typically used for such a task. Stickers are small pieces of wood (usually about 3/4” x 11/2”) that are used to add space between sawn planks, which increases ventilation and aids in a more uniform drying process. Sticker spacing varies depending on the species and thickness of the lumber being dried; a conservative spacing scheme would be every 12”, though usually 16” or 24” spacing can be safely used on thicker pieces.

Add weight. Once the stack of wood is stacked and stickered properly, it’s helpful to add weight to the stack. The lumber at the bottom of the stack is probably weighed down sufficiently by the wood on top of it, but boards near the top greatly benefit from added weight. Weighing the stack of wood down helps to prevent warping or distortion, which is especially important during the initial drying phase when going from green to an ambient EMC. Neatly and properly stacking, stickering, and weighing wood will go a long way towards ensuring that the drying process will result in flat, stable, and usable lumber.

This small stack of Buckthorn (Rhamnus cathartica) half-logs has just been cut, stacked, stickered, and sealed with a water-based wax emulsion coating.

Add heat once EMC is reached. It’s important not to rush the drying process too quickly, but once a wood pile has safely reached EMC, it may be necessary (especially during humid summer months) to bring the MC down even further for a specific project. This can be as simple as moving the lumber stack from a garage or shed into a heated basement indoors. In cases where shorter pieces are used, a drying cabinet can be used to gradually reduce the MC down to 12% mc, 6% mc, or any other level that an application may call for.

A drying cabinet can be nothing more than a simple wood cabinet with an incandescent lightbulb on a dimmer to finely control the light output—which in turn dictates both internal temperature and consequently relative humidity. Many thermometers (both traditional and digital) sold by big-box retailers also feature a hygrometer with a somewhat accurate readout of the relative humidity; the ability to know the rh of both the drying cabinet and the wood shop proves to be a helpful and prudent investment.

Warp and distortion

When a wood species has a high T/R ratio, it will tend to shrink in one dimension more than another while drying, causing distortion or warp. A good way to visualize the tendencies of wood during drying and shrinking is to picture the arc of the growth rings trying to flatten themselves out. (This of course is not actually the cause of the shrinkage, but it serves as a good memory tool to help visualize dimensional changes.)

This endgrain view of Plum exhibits cupping. The board was initially cut flat, with the top and bottom originally being parallel. Further machining will be necessary to ensure the board is flat and square.

The results of uneven shrinkage vary depending upon the particular shape and grain orientation of the board; flatsawn boards become cupped, riftsawn square stock becomes diamond-shaped, and circular dowels become ovoid.

Additionally, there are a number of warping issues that can occur which are not solely related to uneven shrinkage. In certain cases, a pre-existing flaw is present in the wood itself, which is only brought out and made apparent by the drying process. This can result in defects such as: bow, crook, twist, or a combination of two or more defects simultaneously.

Regardless of the specific names that can be applied to distorted lumber, most drying-related warping issues can at least be minimized using a few simple guidelines:

Use proper stacking techniques. As mentioned previously, by far the most important deterrent to warp is the adequate stacking, stickering, and weighing of a lumber stack.

Avoid juvenile wood. Juvenile wood is wood that is formed during a tree’s early years of growth, and can be thought of as an extension of the pith. There is no officially determined width of juvenile wood, (usually excluding the first few central growth rings is sufficient), but generally, the further the wood is cut from the pith, the better. Much like the pith itself, juvenile wood is very unstable, and has an elevated rate of longitudinal shrinkage; this increased shrinkage rate pulls against the mature wood and causes it to contract and deform either along the face of the board (bow), or along the side of the board (crook).

Avoid processing branches or leaning trees. Wood that has been growing at a slant doesn’t have uniform growth ring spacing and varies from the topside to the underside. This abnormal wood is called reaction wood, and it can cause a number of unpredictable warping problems during drying. In softwoods, reaction wood forms on the underside of a branch or trunk, and is called compression wood. Conversely, in hardwoods, just the opposite is true: its reaction wood forms on the topside and is called tension wood.

Avoid knots. Simply put, knots are sections in the trunk where limbs once grew. In addition to shrinking unevenly or possibly coming loose during drying, (leaving a knothole), knots can also create areas of concentrated abnormalities in the wood grain, and consequently impact its shrinkage properties. The presence of large knots can result in dramatic and exaggerated warp during drying.

Handle spiral or interlocked grain with care. Some wood species have what is called spiral or interlocked grain. Just as the name implies, the wood fibers grow in a twisted or interlocking manner. Not surprisingly, this can result in drying problems, most commonly twist—where one of the corners of a board is raised up out of the plane of the other three corners. Careful drying, along with proper stacking, stickering, and weighing can help alleviate difficulties caused by irregular or spiral grain.

The article is clear and concise. I didn’t read this article soon enough. I didn’t seal the ends of my lumber but I will definitely weigh the lumber down.

Donna

I tried beeswax on end grain, but it interfered with finishing and I had to cut off impregnated wood. I decided that sawing off the part of the end grain that has the fast drying cracks was better because I would have to saw off that part anyway if it had the end grain sealer in it. However, it is a question as to how much has to be sawn off to remove the sealer impregnated end, or remove the unsealed cracked end grain.

ejmeier

I’m not sure how far the wax seeped into your wood, but in my experience, it’s maybe 1/4″ at the most. Just about anything will require you to trim at least a little bit off the ends. Beeswax seems like it would be incredibly expensive! You’d be better off just slopping leftover paint on the ends with a brush. (No, honestly, thick coats of paint will do a great job at sealing the endgrain.)

Depending on the wood species, if you don’t seal the ends you could easily lose several inches off the ends, or possibly have it check along the entire length of the board. I’d guess that in all but a few select circumstances you’d end up with more usable wood through sealing.

Tom Zawila

titebond white glue works really well and does not stain as easily. Wax will tend to fall off as the wood shrinks, (by experience). Anchor seal is ok but is not always available and can stain more readily. Good Luck!

PVA wood glue is also a good endgrain sealer. Apply 2 coats and it seems to be working fine on some wood I’m drying for turning. I left 1 small piece unsealed for comparison & this has cracked considerably.

_GA3FAR_

I’m fairly new to this, but If I am to make a drying cabinet like the last paragraph suggests; how long would it take to dry the wood from 12% to 6%?

blackbeered

forever

Rapscalion

This article has answered many of my questions concerning lumber, but i still have a remaining question. What if i want to dry/cure a thin round or cross section from a large diameter tree for the purpose of making a decorative table or clock. Obviously this means the majority of surface area is end grain. Do i still seal it with something, and does that mean that i should cut my round 1/2” to 1” thicker than what the finished thickness will be after it goes through the planer in order to remove the sealer(after curing) for staining purposes?

ejmeier

Endgrain cross sections are notorious for splitting or checking, and the bigger the diameter, the more likely it is to split.

Certain species (Laburnum, Olive, and others) are known to be resistant to splitting. Regardless, I wouldn’t put a sealer on while it’s drying. If I were you, I’d put it inside a brown paper bag, and then put that inside another brown paper bag, stapled or taped shut. This should help regulate and slow the drying process. (BTW, you can’t/shouldn’t plane endgrain.)

jon

ok….ive got green hackberry logs 50 inches thick and 12 feet long….so are you saying they wont check if i dont coat them? where can i get a brown paper bag that large?

ejmeier

My previous reply was in the context of a (relatively) thin piece of wood — in this case, an round endgrain slice. The paper bag technique is used by turners who have already rough-turned their projects down to about 1/2″ to 1″ wall thickness.

In your circumstance, you’d need to seal the logs. I’m not sure if you’re planning on using the logs whole, or if you’re going to cut them up into smaller pieces, but conventional drying wisdom says to slab/cut the log FIRST, and then dry it. Things will be much easier and faster this way.

Don

great article, as “suegatmarois” stated, clear and concise. thank you.

jon

use polyurethane floor sealer, as soon as the wood is cut….hours, better than days after the saw leaves the wood….keep it out of the sun, and wait 2 years…..if you saw logs then get 3 slabs from a log, and good luck……some folks actually soak it in salt water and vinegar for 5 years, and they say when they let it dry, it never checks….kinda like logs in the great lakes, or ocean…

Chris

I find if I leave my logs for the length of time you suggest I find they have been attacked by woodworm. I have also found turning green wood is a waste of time due to twisting and splitting. I get dispondant after turning a bowl for example a split appears either as I am putting the finishing touches or the following day.

ejmeier

Not sure what your procedure is, but generally turning green wood is done in two phases: first a bowl is rough turned to approximate shape, leaving 1/2″ to 1″ wall thickness (more or less depending on overall size). Then the rough blanks are allowed to dry (I put mine in a closed brown paper grocery bag). After the initial drying and slight deformation occurs, the bowl is put back on the lathe for the final turning, sanding, and finishing. Turning a bowl from green to finished product in one shot is asking for disappointment!

Old guy in the woods

One of the last items on my bucket list, is to build a small log cabin, from planted pines, on our property. They are about 8″ diameter. I am 71 so need a quicker solution. What happens if I cut the trees, strip the bark and build the 20′ x30′ cabin in the woods. I have in mind to have the top and bottom, of the logs cut off, leaving a sort-of oblong shape. I intend to have vertical all-thread rod tying the logs together on 4′-6′ centers, so I can tighten nuts on large washers as wood shrinks. Someone told me the frontier folks, cut the trees and built the cabin at the same time.

gregor

you can build with wet logs they will shrink and check naturally don’t worry about it

gregor

Timber frame homes are also built with wet lumber I worked in a timber frame home plant. we cut all the tennons mortises and dove tails and build all trusses from wet lumber.

It is done with wet lumber all the time in Alaska with trees cut processed and used days apart. What you do is set your doors , windows , any opening on a metal case. Leave room (about an inch) all around the metal casing so you rough cut openings will be two inches higher and wider than the window size. You hide the gap with 1×4 trim and when the wood shrinks , your doors will still open and your windows will work. I hope you complete your project and enjoy it soon !

Gordon Hirt

An inch may be OK on the sides of doors and windows but we left a LOT above doors and windows. Green logs can shrink 6-8″ per tall floor depending on the log assembly style (T&G, swedish cope, etc)

Chick from the Sticks

Built a cabin with green logs, pine from my property. Logs were 10″ diameter. Left a good amount of the brownish layer under the bark(I forget what it’s called). Trees were cut in early fall after the weather had cooled a bit and the cabin walls were up by snowfall in November! That was almost 14 years ago. No rot. Some checking for sure, but expected it and it only adds to the rustic charm Go for it Old Guy in the Woods!!!

Deluch

Crazy question but does anyone know the drying time for western red cedar logs, could they be placed in a solar kiln to dry quicker (a big kiln for 10 – 15 logs @ 12-15 inch dia.)? I also hope to build a log home in the next 2 years and have started to research the process from tree to wall…any help would be great.

ejmeier

Round endgrain slices, no matter how slowly they’re dried, have inherent stresses within them. The wood wants to shrink about twice as much tangentially (parallel to the growth rings) than radially (from the center of the disc outward). So being a whole circle without relieving any of the stress is asking for trouble and prevents the natural shrinkage from occurring. A pie-shaped wedge may open up in the endgrain disc, and the larger the diameter of the disc, the more likely and more dramatic will be the split.

tikotongos

i am new in the topic and i would like to know why when i cut my 2′ thick and 5′ width iroko board in 1/2 thick stripes on the bandsaw, the stripes shrink alot. The board is 50′ long! Moisture is about 10%. For me the wood is now useless!!! Can somebody explain me this??? Did i do something wrong or i just didnt choose the correct lumber of iroko??

ejmeier

I’m not clear on the dimensions of your lumber, using the single ‘ denotes feet, not inches. Inches are designed by a double “. I’m guessing you mean you have a board that is 50 inches long, and not 50 feet long.

There’s a lot of reasons why you could be having trouble. What exactly do you mean by “shrinks alot”? If it really is shrinking, I’d guess the wood is not totally dry. But if it is warping or twisting somehow, then that’s another story.

Phillip

I have some sawed cherry lumber that’s been in the barn for 10 years. 1×4’s to 1×8’s. Wanted to use them for flooring but a friend of mine said they’re not dry enough and would warp after planing.
They’ve been through Mississippi summers and I’m wondering if he knows what he’s talking about. Anyone?

ejmeier

How were the boards stored? More than likely, they’ve reached equilibrium moisture content. If you wanted to use them for flooring, I’d recommend storing them inside for a while before you install them. This will allow the wood to acclimate to the humidity level INSIDE your home rather than out in a barn.

Phillip

Stacked and stickered. My dad had them sawed after Hurricane Katrina blew them over.
Are you saying plane them then store them inside?

Jon

Yes that will work. Ten years should be plenty of time for them to dry. I would invest in a moisture meter. I would not use the lumber until it has reached a 10% moisture content. This can be more or less depending on the relative humidity of an area. But after 10 years it will not be drying any further by air drying. I think it will be perfectly fine to use now. Generally wood is air dried for about 1 year per inch of thickness. Then planed and checked for moisture content. Cut an inch or two off the end of the board before checking the moisture content.

Phillip

They were stacked and stickered. Good ventilation I assume.
After they’re planed what would be some things I might encounter? Not a real big woodworker. I prefer metal, you can always add more!

terry

Maybe this is a dumb question, but I plan on building an addition next year, so I have about 12 months between now and when I will be doing the framing. If I were to buy the lumber (2×6’s etc) from the yard now and stack it and sticker it and leave it under cover (in my barn) for that year, will it prevent some of the problems with warping you typically get from typical Home Depot (or wherever) lumber? I’m in Ontario, so humid summers and cold winters, which the stack would experience. I know lumber quality seems to be lower these days, so I was hoping to mitigate that through some prevention, if possible.

ejmeier

Probably couldn’t hurt. Not 100% sure though: maybe the distortion is caused by knots/defects in the wood itself…

Jesse Francis

Exactly what is a “water based wax emulsion” and under what product name(s) may I find it? I can only find floor sealers and the like, nothing as thick or opaque as pictured above.

so i have cedar in my woods that has been laying there almost 30 years (when they cleared the property to biuld the house) can i just get this and start making stuff with it?

ejmeier

Are you talking about cedar lumber, or just a raw cedar log? 30 years is a long time… I would take a look at it first and see what kind of condition it’s in. If nothing else, you’d probably want to let it air dry and let the moisture level even out across the length and width of the board(s).